Spinneret pack for flash extrusion



Dec. 23, 1969 J. G. SMITH SPINNERET PACK FOR FLASH EXTRUSION 3Sheets-Sheet 1 Filed .April 6, 1967 1969 J. G. SMITH 3,484,899

SPINNERET PACK FOR FLASH EXTRUSION Filed April 6, 1967 3 Sheets-Sheet 2Dec. 23, 1969 J. G. SMITH 3,484,899

SPINNERET PACK FOR FLASH EXTRUSION Filed April 6, 1967 3 Sheets-Sheet 5United States Patent 3,484,899 SPINNERET PACK FOR FLASH EXTRUSION JamesGerald Smith, Newark, Del., assignor to E. I. du

Pont de Nemours and Company, Wilmington, DeL, a

corporation of Delaware Filed Apr. 6, 1967, 523'. l *0. 628,888 Int. Cl.Dtlld 3/00 U.S. Cl. 188 6 Claims ABSTRACT OF THE DISCLOSURE A spinneretpack for flash-spinning including an L- shaped structure and anattachment block. Passageways for polymer solution and heating fluid areprovided in the L-shaped structure and these communicate with ports inthe attachment block, which in turn communicate with corresponding portsin a fixed mounting block. The pack can be accurately positioned in aspinning cell by aligning guides on the attachment and mounting blocks.

BACKGROUND OF THE INVENTION The present invention is concerned with aspinneret pack for producing synthetic filamentary material and moreparticularly with a spinneret pack for flash-extruding a polymersolution to form a plexifilamentary strand The art of flash-extruding orflash-spinning is described in U.S. Patent 3,081,519 to Blades andWhite. In essence, it comprises spinning a solution of polymer which isforwarded continuously to the spinneret at a temperature above theboiling point of the solvent. Preferabl the temperature is near thecritical temperature of the solvent. In the spinneret pack the solutionis kept at a pressure considerably above the autogenous pressure, eg, bymechanical means described in U.S. Patent 3,227,794 to Anderson andRomano. The pressurized hot solution is fed to an orifice which is muchlarger than the usual orifice for dry spinning or wet spinning. As thesolution extrudes from the spinneret orifice, the solvent expandsrapidly into a gas. Bubbles are formed which expand and grow while beingcooled adiabatically. When the temperature of the spinning solution issufliciently high and when the concentration is sufliciently low, thesolvent gas expands sufiiciently to rupture the bubbles and form afibrillated strand which has been termed a plexifilament. The strand iscomposed of a 3-dimensional network of film-fibril elements which areconnected at tie points along and across the strand. The film-fibrilelements are less than microns thick. In general, the spinnerets usedfor flash-spinning have a single large orifice. A mulifibrous strand isthus obtained from a single orifice. It should be evident thatspinnerets entirely different from those used in wet or dry spinningmust be designed for flashspinning. Some of the earlier spinnerets aredescribed in the Blades and White patent.

Additional spinneret art is disclosed in U.S. Patent 3,169,899 toSteuber. This patent discloses spinnerets which are horizontallyoriented and which direct the strand against an oscillating baflle,which, in turn, spreads the strand into a Wide network which isdeposited on a moving belt. A fibrous sheet is obtained having networksoriented in an overlapping multi-directional configuration. The fibroussheet is useful for preparation of wall covering, book binding, softtextile like nonwovens, and as a substrate for various coatings,impregnants, and laminates.

In developing the flash spinning technology for preparation of nonwovenfibrous sheets, it has become obvious that improved spinnerets areneeded. In particular, when a large number of spinnerets are used fordeposit of the plexifilaments on a moving belt, these must be accuratelypositioned and coordinated to produce a uniform deposit.

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In addition, it has been discovered that the solvent gases, which arevolatilized almost explosively, create considerable turbulence in theflash spinning chamber. For this reason, the design of the entireapparatus must be directed toward streamlined flow.

SUMMARY OF THE INVENTION According to this invention there is provided aspinneret pack for flash-extrusion of a polymer solution to form aplexifilamentary strand. The spinneret can be readily and accuratelypositioned in the ceiling of a flash spinning cell. It is simple toremove and replace in the cell and it minimizes the effect ofgasturbulence within the cell. Reduced turbulence serves to reduce foldingand entanglement of the plexifilament and accurate placement serves togive accurate regulation of the overlapping deposits on a moving belt.

The spinneret pack of this invention comprises an L shaped solutionsupply tube having a vertical mounting arm and a tapered horizontalextrusion arm and having passageways for polymer solution and heatexchange fluid. An attachment block is rigidly mounted on the upper endof the vertical arm. The attachment block is provided with a portcommunicating with the passageway for polymer solution in the L-shapedtube and additional ports for heat exchange fluid inlet and outletcommunicating with the passageway for heat exchange fluid in theL-shaped tube. All of the ports in the attachment block terminate in acommon surface; the spinneret pack is mounted in the ceiling of aspinning cell by mating this surface of the attachment block with asimilar surface of a rigid mounting block having corresponding ports forpolymer solution and for heat exchange fluid inlet and outlet.

BRIEF DESCRIPTION OR THE DRAWINGS FIGURE 1 is a side elevation showingthe apparatus of the invention.

FIGURE 2 is an end view of the same apparatus.

FIGURE 3 is a cross-sectional view taken along the line 33 of FIGURE 2.

FIGURE 4 is a side elevation of a valve unit which serves as a mountingblock to align the apparatus of FIG- URES l, 2, and 3.

FIGURE 5 is a cross-setcional elevation view of the spinning arm portionof the L-shaped solution supply tube.

FIGURE 6 is a diagram showing the positioning of the spinneret noseopposite a rotating baflie. The location of an ion gun for depositing anelectrostatic charge is also shown.

DETAILED DESCRIPTION Considering FIGURE 1, the flash-extrusion spinneretpack comprises an L-shaped solution supply tube 10 having verticalmounting arm 12 and a horizontal spinning arm 14. A plate 16 is providedon vertical arm 12; this plate rests lightly upon a gasket around a holein a supporting plate. The supporting plate in turn rests on a gasketaround a port hole in the ceiling of a spinning chamber. The entire unitis fastened and supported in precise spinning position by means ofattachment block 18. The attachment block is provided with a solutioninlet port 20, a steam inlet port 22, and a steam outlet port 24, all ofthese being gasketed.

The vertical location of the spinneret above the moving collection belt(not shown) is established by means of a carefully milled notch 28 shownin FIGURE 2 by means of dotted lines. The notch is located in block 26,which is bolted to attachment block 18. A matching lip is provided onthe flange of a valve shown in FIGURE 4. The valve serves as a positiveguide for locating the position of the spinneret pack over thecollecting belt. Cover plates 30 in FIGURES 1, 2 and 3 are side guideswhich help to position the spinneret pack when it is lowered by craneonto the lip. The approximate location of the spinneret pack in thelongitudinal direction along the collection belt is fixed by bolt holes32 (FIGURES l and 3). Mounting bolts 34 (FIGURE 2) are screwed throughthese holes into the rigidly supported valve shown in FIGURE 4. Thevalve unit is steam cored. The solution inlet port 20 for the spinneretpack when mounted coincides with the solution outlet port of the valve(FIGURE 4). The steam inlet port 22 and steam outlet port 24 coincidewith the corresponding steam lines in the valve. The three connectionsare gasketed by means of rings not shown. The surface 36 of thespinneret pack assembly is machined to mate precisely with the fiat faceof the flange on the solution and steam supply valve.

During the mounting process the spinneret pack of FIGURE 2 is lowered insuch a manner that the precise groove 28 falls over the top of the lip69 of the valve shown in FIGURE 4. The top of the lip is carefullymilled and permanently positioned so that it will be parallel to thesurface of the moving belt. The top of the milled notch 28 in theattachment block 18 of FIGURE 2 is precisely parallel to the spinneretorifice axis 63. When the notch 28 of the spinneret pack assembly isprecisely located on the lip of the mounting unit, the unit is properlyoriented for spinning. The precise matching of the lip and the groovecan be determined by means of feeler buttons 38 which are carefullymachined. After properly orienting the pack, bolts 34 are passed throughholes 32 and screwed into matching holes in the valve flange.

In the spinning arm 14 of FIG. 3 a fitting 40 is provided for measuringpressure in a chamber of the spinneret to be described. A- flexiblemercury capillary 42 transmits this pressure to a pressure transducer.The capillary is located in a flexible tube. Massive plates 44 which arewelded to the solution supply tube are provided for stiffening thestructure and may also be used for supporting deflector positioningequipment (not shown) which, in turn, supports a web deflector unit andweb charging unit. The location of the deflector and charging unitsrelative to the spinneret is shown in FIGURE 6. The complex positioningequipment is omitted for clarity; it is described in detail in the US.application of James Gerald Smith, Ser. No. 628,872, filedsimultaneously herewith.

It should be noted that horizontal spinning arm 14 is tapered toward thespinneret orifice 11. Likewise, a tapered nose piece 13 is provided. Asshown in FIGURE 2, the tapered spinning arm 14 has recesses for bolts15. The tapered pieces are generally conical but could be wedge-shaped,if desired. The amount of interrupted surface should be minimized topromote streamlined flow.

Considering further the mounting system, FIGURE 2, shows by means ofdotted lines the location of passageways in the attachment block 18:solution inlet port 20, steam inlet port 22, and steam outlet port 24.The main solution inlet 20 empties into an annular zone around a filterin the upper end of the vertical mounting arm 12. This solution entrypoint is indicated by the number 17 in FIGURE 3. The steam inlet 22empties into a different annular area which is indicated in FIGURE 3 bythe number 19. The steam outlet 24 of FIGURE 2 carries steam from pipe21. The steam inflow and outflow passageways are connected to separatepassageways in the valve which serves as mounting block for thespinneret pack.

In FIGURE 3 a cross-section is shown for the spinneret pack assembly.The exterior parts are the same as those in FIGURES 1 and 2. The view isfrom the reverse side compared to FIGURE 1. Cap 23 is the upper portionof a cylindrical solution filter 25 which screws into the end ofvertical mounting arm 12. This cap is also provided with screw threadsby which an eye bolt 27 may be attached for lifting the unit. Inside thecap 23 is a gasket for sealing the cap and filter. The filter comprisesa cylindrical screen 29, which is sealed to an upper cylinder 31, and alower cylinder 33. A perforated cylinder 35 is attached and sealed tothe upper cylinder 31. Stiffening rings 37 on the perforated cylinderprevent collapse of the screen when exposed to exterior pressure. Thelower cylinder 33 of the filter is sealed to the perforated cylinder 35.The lower end of the filter unit when installedis sealed by gasket 39 tothe pipe 41. Pipe 41 is constructed of very thick material to providestiffness.

In operation of the apparatus solution is pumped from the inlet port 20through annular space 17. It passes inward through screen 29' andperforated tube 35. The filtered solution then passes downward throughpipe 41 to the tubular L-bend 43. The solution then passes to thetapered horizontal spinning arm 14 through approach insert 45.

The steam supply for the spinneret pack is provided through annularpassage 19. It passes downward through the outside passageway to chamber46 and into the horizontal spinning arm 14 through passageway 47.Chamber 46 because of sloping partition 48 permits condensed steam to becarried completely out of the vertical arm 12. The steam passes throughpassageway 49 in spinning arm 14, circles the arm near the nose of thespinneret and returns through passageways 50 and 51 into chamber 52 andeventually out through tube 21. Needle valves are used to allow aconstant steam bleed through; the moving steam entrains the condensateand blows it upward through line 21 and out of the spin pack.

A very useful feature of the apparatus is its adaptability for spinningat a variety of flow rates. In the Anderson and Romano patent, referredto above, the importance of a pressure let-down chamber is indicated.Likewise, the residence time in this chamber is mentioned as animportant process element. The assembly of inserts in the horizontalspinning arm 14 permits a variety of spinning rates to be used withoutchanges in the spinneret exterior. Exterior changes must be minimized sothat the stream-lined flow is maintained and so that the position of thetapered spinneret nose 13 opposite the web deflector will be maintained.The entire horizontal spinning arm 14 is mounted on the verticalmounting arm 12 by means of bolts 15, which pass through the mainexterior piece 53. Approach insert 45 and retainer insert 54 togethermust fill the cavity between the shoulder 55 and the end of L-bendsupply pipe 43. A let-down orifice 56 is provided between inserts 45 and54.

A let-down chamber 57 following orifice 56 permits nucleation of thespinning solution as described in the Anderson and Romano patentreferred to above. When the solution, for example, is 12.5% linearpolyethylene in trichlorofluoromethane and is supplied to the let-downorifice 56 at 1600 p.s.i.g. (113 kg/cmf"), a single phase liquid ispresent upstream of the let-down orifice. The pressure in the chamber 57is typically about 900 p.s.i.g. (63.4 kg./cm. and a two-liquid-phasedispersion exists downstream from orifice 56.

The spinning arm 14 is shown in somewhat greater detail in FIG. 5. Itwill be observed that supported between approach insert 45 and retainerinsert 54 is a disc 58 having a hole which comprises let-down orifice56. The solution (actually a two-liquid-phase dispersion) in let-downchamber 57 passes through screen insert 59, the

I screen being fused to the end of a cylindrical tube 80. A

final orifice approach insert 60 conducts the solution to disc 61 havinga hole comprising the exit orifice 11. Disc 61 is concentrically locatedrelative to the conical taper of the approach insert 60.

Inserts 59, 60 and 61 are fastened into the horizontal spinning arm 14by means of tapered nose piece 13. Nose piece 13 is threaded ontoexterior piece 53. Nose piece 13 has a centrally drilled hole whichserves as a tunnel 62 for the solution as it is spun. The finalspinneret disc 61 must be carefully centered so that the orifice 11 isconcentric with the cylindrical tunnel 62.

The solution is extruded from the final orifice 11 and the solventevaporates spontaneously, resulting in precipitation of the polymerwhich expands and fills tunnel 62. As it issues from the tunnel, thepolymer is in the form of a plexifilamentary strand. In FIGURE 6 thisstrand (not shown) is passed directly to a rotating lobed deflector 64.Because of the contours in the deflector surface the strand is directedalternately to the left and to the right as it descends to the movingbelt not shown. Simultaneously, the strand is spread into a widenetwork. The network passes over a target plate 65 which is grounded.Ion gun 66 which is charged to a voltage of 30 to 70 kilovolts deposits9. charge on the network causing it to remain in the spread-openconfiguration as it falls to a moving belt. The network is collected onthe moving belt. Preferably, the belt is an electro-conductive materialand is charged oppositely to the fibers.

By placing various combinations of insert pairs 45 and 54 in the nozzlea variety of flow rates may be used with a high degree of fibrillationbeing maintained in each case. For example, to use a higher flow rate ashorter approach insert 45 is used and a longer retainer insert 54 isused. In this way the let-down orifice is moved upstream and a largerlet-down chamber is formed. The larger chamber compensates for higherflow rates. The exposure time in the let-down chamber may be thusadjusted to the same level for various flow rates. Of course, inserts 45and 54 should be matched so that the cavity between shoulder 55 and theend of L-bend supply tube 43 will be properly filled and sealed. Forconvenience, it is usually preferred to assemble all of the parts of thehorizontal spinning arm 14 first and then to mount these by means ofbolts 15 in one operation. After this, the pressure sensor fitting 40 isinstalled and connected by capillary 42 to a transducer.

As stated above, the spinneret pack may be used as the support structurefor a rotary web deflector and position ing equipment to accuratelyestablish the relative locations of the web deflector centerlineopposite the final orifice centerline. This equipment may beconveniently connected to the upper mounting arm of the spinneret packassembly by attachment to bracket 44. When connected in this way, thespinneret pack assembly, the web deflector and positioning equipment maybe removed from the ceiling of a spinning chamber in one simpleoperation.

The rapid removal of the spinneret pack is greatly facilitated by havingall fluid conduits communicate with ports in the attachment block 18which ports terminate in a common surface 36. As shown in FIGURE 4, thesurface 36 mates with a similar surface of a mounting block 70 havingcorresponding ports. The ports are not shown in FIG. 4 but are aligned,for example, as shown in FIGS. 1-3. Bolts 34 extend through attachmentblock 18 and into the surface of mounting block 70. The spinneret packcan be removed from the spinning cell merely by removing bolts 34, thenlifting by means of a hook not shown attached to plate 67 and locatedover the center of gravity of the pack-deflector unit (when the wholeunit is to be removed) or attached to cap 23 (when the spinneret packonly is to be removed).

As shown in FIG. 4, mounting block 70 can be part of a heated valveunit. In the embodiment shown a jacketed line 72 supplies polymersolution to valve body 71. A primer such as nitrogen is introducedthrough line 73. Heat exchange fluid is supplied through line 100 andremoved through line 101. A three-way valve in valve body 71 admitseither nitrogen or polymer solution to the port 20 leading to thecentral conduit in the vertical arm 12 of the L-shaped solution supplytube (FIG. 1). Use of nitrogen as a primer in starting upflash-extrusion operations is described and claimed in Gilardi U.S.application Ser. No. 607,304, filed Ian. 4, 1967. The valve body alsocontains passages (not shown) for circulation of heat exchange fluid,and the valve unit also includes inlet and outlet lines (not shown)carrying heating fluid.

The valve unit is supported on plate 78 which is in turn supportedthrough jack screws 74 on block 76. Position of the valve unit andassociated mounting block is accurately adjusted by means of jack screws74 and fastened by screws 75. Block 76 is supported upon ceilingstructure 77 of the spinning cell.

Once the flash-spinning unit has been removed from the spinning chamber,it may be serviced in any way needed. It should be pointed out that theassembly which supports deflector 64 (FIG. 6) must be carefullypositioned and rigidly supported opposite the spinneret orifice. If thedeflector assembly is attached to the spinneret pack through massiveplates 44 (FIGS 1 and 2) the latter may be disassembled withoutcompletely dismantling the former. Thus, as described in the Smithapplication Ser. No. 628,872, referred to above, the web deflector unitand positioning equipment can be separated from the spinneret pack byremoval of bolts in bracket 44, and can be separately supported bystructure connected to the sup-porting plate for the integral unit. Thespinneret pack can then be lifted separately by a crane attached to aneye bolt 27 screwed into a threaded socket in cap 23.

The filter unit 25 may be removed without removing the various insertsin the horizontal arm. Likewise, the inserts defining the let-downchamber may be replaced without the necessity of removing the filter. Itshould be understood however that the most thorough procedure consistsin removing and separating all of the parts in the vertical andhorizontal arms of the spinneret pack assembly. The present inventionprovides ra-pid servicing and cleaning of all parts and minimizes theamount of effort which is needed for cleaning crevasses and hiddencavities.

I claim:

1. A (spinneret pack for flash-extruding a polymer solution to form aplexifilamentary strand comprising an L-shaped solution supply tubehaving a vertical mounting arm and a horizontal extrusion arm, thevertical :arm having a central conduit for polymer solution and anannular conduit for heat exchange fluid, the horizontal arm beingrigidly mounted on the vertical arm but capable of being detachedtherefrom, the horizontal arm having a central conduit for polymersolution which communicates with the central conduit in the vertical armand terminates in an extrusion orifice, and a separate conduit for heatexchange fluid which communicates with the annular conduit in thevertical arm, the central conduit in the horizontal arm containing apair of removable sleeve inserts which hold in place between them a dischaving a central hole, thereby dividing the central conduit into twochambers connected by an orifice, the exterior of the horizontal armbeing tapered toward the extrusion orifice to minimize turbulence;

an attachment block rigidly mounted on the upper end of the verticalmounting arm and having a port communicating with the conduit forpolymer solution and having additional ports for heat exchange fluidinlet and outlet communicating with the conduit for heat exchange fluidin the L-shaped solution supply tube, all of the ports terminating in acommon surface on the attachment block, the pack being mountable in theceiling of a spinning cell by mating that surface with a similar surfaceof a rigid mounting block having corresponding ports for polymersolution and for heat exchange fluid inlet and outlet.

2. A spinneret pack as defined in claim 1 wherein a pipe external to theL-shaped solution supply tube connects the conduit for heat exchangefluid in the horizontal arm with the outlet port for heat exchange fluidin the attachment block.

3. A spinneret pack as defined in claim 1 wherein the attachment blockhas a groove which is machined to mate precisely with a lip on themounting block, the tops of both groove and lip being substantiallyparallel to a horizontal plane containing the longitudinal axis of thespinning arm, said groove and lip providing for exact positioning of thespinneret pack relative to the rigid mounting block.

4. A spinneret pack as defined in claim 3 wherein means are provided forrigidly attaching the spinneret pack to the mounting block.

5. A spinneret pack as defined in claim 2 wherein the attachment blockhas a groove which is machined to mate precisely with a lip on themounting block, the tops of both groove and lip being substantiallyparallel to a horizontal plane containing the longitudinal axis of thespinning arm, said groove and lip providing for exact posi- ReferencesCited UNITED STATES PATENTS 702,382 6/ 1902 Topham. 2,136,201 11/1938Whitehead. 2,586,971 2/ 1952 MCDCIIIIOUZ. 2,821,743 2/1958 Kocay.2,917,327 12/ 1959 McDermott et a1. 3,176,345 4/1965 Powell.

WILLIAM J. STEPHENSON, Primary Examiner

